1. Field of the Invention
The invention relates to a method for monitoring the operational state of electric motors, and a circuit arrangement for executing the method.
2. Description of the Related Art
It is known that safety functions are increasingly provided for the most varied types of machine tools and processing centers, which as a rule assures a limited operation, a safe stop or safe operating stop of the respective machines even if one or several components fail, or in case of wrong operation. By means of this it is intended to dependably prevent accidents in which the workpiece, the tool or the machine could be damaged or the user could even be injured. To avoid expensive additional arrangements, these safety functions are integrated into the control unit of the machine.
So that the control unit of the machine can dependably detect at what time it is necessary to perform a safety function, the functions and parameters relevant for safety are also positively monitored. To this end, it is necessary that two independent processors perform the monitoring actions simultaneously.
It is disadvantageous here that up to now only the safe processing and the safe forwarding of the signals received from an electric motor or transmitted to an electric motor were monitored. If operational states should occur inside the electric motor itself which might lead to an unsafe operational state of the entire machine, this cannot be detected by the control unit, since in this case there is no erroneous processing or transmission.